High Sierra Mail crashes upon retrieving certain messages

High Sierra Mail (Ver 11.2 (3445.5.20) and earlier) crashes and provides a CDA report that I've been sending to apple every time it crashes. The same exact configuration does not crash when reading the exact same messages on Mac Mail (Ver 10.3 (3273)). If I move the messages to a subfolder (on another computer), eventually High Sierra Mail doesn't crash upon startup. I've rebuilt the folders. Deleted the indexes. And followed the advice from several other reports. However, eventually a message arrives that HS Mail can't process and it crashes.. and I have to repeat the process all over again.

As a former QA tester, I believe I've collected the data needed and even have isolated an email that causes the crash. (which, btw, the header data looks just fine - but clearly something is malformed for HS Mail to process it without crashing.)

How does one open a case with Apple? Do they monitor this site? Another report of this problem has at least 20 people with the same issue, and yet... It remains unaddressed.